1. Technical Field
The present disclosure relates generally to a visual drive control method and apparatus, and more particularly to a visual drive control method and apparatus with multi-phase encoding.
2. Description of Related Art
In the past decades, brain computer interface (BCI) systems with steady-state visual evoked potential (SSVEP) are developed and utilized in the biomedical field, and they are also utilized widely to control the driving control interface of the specific devices for people unable to move freely. A frequency-tagged signal and/or a phase-tagged signal are adopted as a signal source of a flicker displaying device, used as visual targets, for the steady-state visual evoked potential method.
When the steady-state visual evoked potential method with the frequency-tagged signal is adopted in the brain computer interface system, optic nerve of an organism is evoked by the visual targets, which have different frequencies, in order to generate brain wave signals related to the frequencies of the visual targets. However, the visual targets under several different frequencies will cause the visual display to be messy, and tend to cause the visual fatigue for the user.
On the other hand, when the steady-state visual evoked potential method with the phase-tagged signal is adopted in the brain computer interface system, the optic nerve of the organism is evoked by the visual targets, which have different phases, in order to generate the brain wave signals related to the phases of the visual targets. The visual display is less messy due to the visual targets have the same frequency, and has the advantage of less visual fatigue for viewers. However, a calibration process has to be performed to the phases of the visual targets and the phases of the brain wave signals to find out a specific reference phase of the brain wave signals for each user before using the brain computer interface system with phase-tagged signal. Because the user adaptations of the visual targets are not the same, a phase shift is generated in the reference phase of the brain wave signal of the user after a long term of visual stimulation, such that the phase shift between the phases of the visual targets and the phases of the brain wave signals has to be calibrated frequently in the brain computer interface system with phase-tagged signal to acquire a correct correlation between the phases of the brain wave signals and the phases of the visual targets.
Therefore, the brain computer interface systems have less visual fatigue to the user, but it cause the inconvenience of operating the brain computer interface systems with phase calibration process which has to be improved necessarily.